Airbag devices have almost become standard equipment in recent vehicles. An airbag device is a safety device which operates during an emergency such as a vehicle collision and which expands and deploys under gas pressure to receive and protect an occupant. Airbag devices come in various types in accordance with installation locations or applications. For example, in order to protect occupants of front seats from impact mainly in a longitudinal direction (i.e. frontal impacts), a driver's seat is provided with a front airbag at a center of a steering wheel while a passenger airbag is provided in a vicinity of a passenger seat inside an instrument panel or at another location. In addition, in order to protect respective occupants of front and back row seats from a side collision or from a subsequently occurring rollover (overturn), a curtain airbag which expands and deploys along a side window is provided in a vicinity of a ceiling of a wall part, and a side airbag which expands and deploys to an immediate side of an occupant is provided in a side part of a seat.
Generally, a passenger seat airbag device adopts a structure in which an inflator that generates expansion gas and an airbag that expands and deploys due to the gas are housed inside an instrument panel. During a collision of a vehicle, the inflator operates to expand the airbag, and the airbag deploys toward the inside of the vehicle to restrain a forward movement of an occupant.
In airbag development, there are constant demands for improving occupant restraining performance. For example, a passenger seat airbag device disclosed in Japanese Patent Application Laid-open No. 2006-88856 is configured such that shapes of left and right expanding portions in a vehicle width direction differ from each other. In the above cited reference, since shapes and positions (shapes inside cabin) of various windows and pillars are bilaterally asymmetrical from the perspective of an occupant sitting on a seat, occupant restraining performance is improved by giving left and right expanding portions different shapes in accordance with the bilateral asymmetry.
In addition, in recent years, enhanced occupant protection is increasingly being required in various collision modes including, in addition to a head-on collision in which a vehicle collides head-on with an obstacle (an oncoming vehicle or the like), a case where an obstacle collides with a part of a vehicle (an offset collision) and a case where a part of a vehicle collides with an obstacle from an oblique direction.
Referring to the appended drawings, FIG. 1 is a plan view which shows a structure of a conventional vehicle (a left-hand drive vehicle) including airbag devices for a driver's seat and a passenger seat and which shows a situation where the vehicle is approaching, at an angle of 0 degrees, an object (an obstacle) at a position deviated from directly in front. A driver's seat airbag 16 is housed inside a steering wheel 14 in front of a driver 10 and is configured to deploy toward an occupant when a collision occurs. A passenger seat airbag 18 is housed inside an instrument panel 24 in front of an occupant 12 of the passenger seat and is configured to deploy toward the occupant when a collision occurs. The airbags 14 and 18 are configured to expand due to expansion gas supplied from an inflator (not shown) which is operated by a signal of a collision sensor.
FIG. 2 is a plan view which shows a structure of a conventional vehicle mounted with airbag devices for a driver's seat and a passenger seat and which shows a situation where the vehicle is approaching, at a prescribed angle θ, an object (an obstacle) at a position deviated from directly in front. FIG. 3 shows a situation where a vehicle body rotates after colliding with the object (an obstacle) in the state shown in FIG. 2. In a situation such as that shown in FIG. 3, there is a risk that the occupant 12 of the passenger seat may slide across the side of passenger seat airbag 18 and collide with a center console between the driver's seat and the passenger seat. In this case, in addition to an injury caused by a direct collision with the center console, the occupant 12 may suffer brain damage due to a rotation of the head. A brain damage index thereof is referred to as BRIC (Brain Rotational Injury Criteria).